Stabilization of vinyl compounds



Patented Jan. 11, 1949 STABILIZATION OF VINYL COMPOUNDS John R. Durland, Nitro, W. Van, assignor to Monsanto Chemical Company, St. Louis, Mo., a. corporation of Delaware Application September 21,1946, SerialNo. 698,482 I No Drawing.

2 Claims. (Cl. 260-6665) The present invention relates to the stabilization of vinyl compounds and to the stabilized compositions so produced.

It is well known that vinyl compounds as for example vinyl esters, and vinyl aromatic compounds such as styrene, its homologues and analogues tend to polymerize on standing. In the manufacture of vinyl polymers premature polymerization even to a very slight extent may render the monomer unfit for use since it may seriously affect the properties of the finally polymerized product. For this and other reasons it is essential to prevent premature polymerization and for this purpose it is common practice to add an inhibiting agent to the liquid monomer. An object of this invention is to provide a new and improved class ofinhibiting agents.

A further object of the invention is to provide a class of cheap materials which are effective inhibiting agents. A still further object is to provide a class of inhibiting agents which are easily removable from the liquid monomer after which the polymerization reaction can be carried out in I a normal manner. Other and further objects will be apparent from the description following.

In accordance with this invention it has been found that phenolic sulfides effectively inhibit the polymerization of vinyl compounds during storage, shipment and distillation. The monosultides are the most eiiective and are therefore preferred but higher sulfides as for example disulfides and polysulfides of phenols can be used with 7 good results. One or more hydroxy groups may be present in the aromatic nucleus as well as other substituents such as alkoxy, alkyl and halogen pounds have been found to possess marked inhibitlng action when incorporated into monomeric styrene. It is to be understood that the above are merely illustrative of the invention and other phenolic sulfides can be used where convenient or desirable.

The phenolic sulfides do not discolor vinyl compounds and are therefore eminently suitable for incorporating into the compositions prior to storage. In addition, they are effective at elevated temperatures as for example 100 C.-200 C. as well as at storage temperatures and eflectively prevent polymerization during distillation. They are easily removed during distillation of the vinyl compound and in nowlse affect the polymerization of the distilled products. The amount of inhibitor to be used will of course vary according to the particular composition and conditions under which it is to be used but in general proportions within the range of 0.001 to 5% are satisfactory. Often the merest traces are suflicient to prevent polymerization entirely.

Among vinyl monomers which can be preserved by incorporating therein a phenolic sulfide are vinyl acetate, divinyl benzene, a methyl styrene,

. p-methyl styrene, ethyl vinyl benzene, vinyl naphthalene, p-chloro styrene and the like.

- As specific examples of the invention which illustrate the inhibiting power of phenolic sulfides but which are not to "be taken as limitative of the invention, 0.250 part by weight of inhibitor was charged with 25 parts by weight of freshly distilled styrene into screw cap bottles oi suitable groups. In general, the phenolic sulfides possess the type formula (0H) nR1sz.-R(oH)7i where a: and n are integers or polymers of this nucleus,

(OH) nRSr-R(OH) n-SR(OH) 11, etc.

Typical examples of phenolic sulfides which can be used in the practice of this invention comprise the following: di-(o-benzyl phenol) monocarvacrol monosulfide; di-catechol disulfide; dicatechol monosulfide; di-m-cresol monosulfide; di-o-cresol monosulfide; di(di-t-butyl catechol) monosulfide; di-p-hydroxy naphthyl disulfide; di-phenol monosulfide; di-thymol monosulfide; monosulfide of catechol monobenzyl ether; dihydroquinone disulfide and di(2-methyl, 4 tbutyl) phenol disulfide. All'of the foregoing comcapacity having the caps lined with tin foil. The

' samples were then immersed in a boiling water bath for a total of 20 hours. Viscosity tests were then made at 25 C. with a 10 ml. analytical pipette measuring the time of flow from the upper mark to a lower mark just belowthe bulb. For monomeric styrene the time of flow was 11.5 seconds. The viscosities in the table below are expressed as relative values with monomeric-styrene as one. As a further measure of the inhibitin action the polystyrene content was determined by distillation.-

Relative Polystyrene, mmbimr viscosity percent Di-(p. t-butyl oatechol) monosulfide 1.01 0. 30 Di-catechol monosulfldo 1. 02 0. 45 Di-m-cresol monosulflde... l. 02- 0.85 Dl-o-cresol monosulfide l. 10 0.50 Di-thymol monosuliide l. 03 0. Monosulflde oi catecbol monobcnz other 1.00 0.05

By way of comparison styrene without an inhibitor was too viscous for test after heating for the same, length of time.

Storage tests were carried out employing phenolic sulfides as storage inhibitors. Freshly dis- 5 tilled styrene was stored in the dark at approximately 25 C. in contact with 24 gauge sheet steel. 0.01% of inhibitor was incorporated into the styrene and samples tested periodically for increase in viscosity. The condition of the styrene showed 10 no change after many months storage. The results are summarized below:

- carvacrol, thymol, m-ciesol, and p-tertiary butyi m-cresol preserved styrene without noticeable change for long-periods of time. After more than three years storage the styrene containing these materials 'still retained its original colorless form and fluidity.

Again. the invention is not limited to the compositions set forth to illustrate the invention. Other polymerizable vinyl compounds can be stabilized with the new inhibitors and other phenolic sulfides used. The method 01' adding the inhibitor can be varied widely.

The addition of the inhibitor caused no discoloration and as shown by the above data there was no evidence oi. discoloration after long periods of storage. I small proportions of phenolic sulfides eflectively preserve styrene during storage. In this connection, mention should be made of the fact that the inhibitors may be employed in proportion sufllcient to stabilize the vinyl compound at room 35 temperature, or thereabout, out in proportion insuflicient to stabilize the composition at elevated temperature, in which case the stabilizing agent need not be removed. Instead, the composition These results show that very 30 This is a continuation-in-part of co-pending application Serial No. 524,637, filed March 1, 1944, now Patent 2,410,408.

This invention is limited solely by the claims taittached hereto as part of the present specifica- What is claimed is:

1. A liquid composition comprising monomeric styrene and a proportion of di-(p. tert. butyl meta cresol) monosulfide sufllcient to inhibit polymerization.

2. Aliquid composition comprising a styrene monomer and a proportion sufllcient to inhibit may e heated to produce Polymeric Products in polymerization of a monosulflde of mono butylthe presence of the stabilizing agent. Contrary to expectations, the phenolic sulfides which are the most effective inhibitors at elevated temperature are not necessarily the most efiective at storage temperatures. Thus, sulfides of certain cresols while somewhat less active than the polyhydric phenol sulfides at elevated temperature are as effective as any storage inhibitors known.

A large number of phenolic sulfides have been 50 Number tested and found to possess inhibiting action in every instance but only the monosulfldes of ated meta cresol.

JOHN R. DURLAND.

REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS Country Date 496,966 Great Britain Dec. 9, 1938 

